1. Field of the Invention
The present invention relates to a water-based ink for ink-jet recording, an ink-jet recording process, a recording unit, an ink cartridge and an ink-jet recording apparatus.
2. Related Background Art
An ink-jet recording system is a recording system that fine ink droplets are formed by one of various methods, and the ink droplets are directly applied to a recording medium such as paper. Water-based inks are principally used as ink-jet recording inks from the viewpoints of safety, odor and the like. These inks are composed of a water-soluble dye or pigment, a water-soluble organic solvent (anti-crusting agent) used for preventing clogging by drying within an ejection nozzle, water, and optional components such as a penetrant, a dye-dissolving aid and a mildewproofing agent.
With the development of high-performance personal computers and the standardization of GUI environment, performance required of ink-jet inks includes the compatibility of high-sped printing with image quality. In particular, performance required of coloring materials includes reliability, coloration, fastness properties and the like. In response to these performance requirements, direct dyes and acid dyes have been used to date. However, the use of these dyes has been unable to achieve satisfactory performance in fastness properties in particular. Recently, pigment inks of a black color have been commercialized, and image quality and coloration have been improved. However, such a pigment ink is poor in reliability compared with dye inks. Color pigments such as yellow, cyan and magenta pigments are excellent in fastness properties, but poor in light transmission property, and are difficult to reach the level of dyes in coloration, to say nothing of reliability.
Various dyes (reactive dyes) having a reactive group in their molecules are coloring materials excellent in reliability, coloration, light fastness, resistance to ozone, etc. In recent years, it has been attempted to react these reactive dyes with a polymer to improve their water fastness, so as to use the reaction products as coloring materials for ink-jet. For example, in Japanese Patent Publication No. 62-16232, dyes having a chlorotriazine or vinylsulfone group are reacted with a polyhydric alcohol or formamide to use the reaction products as coloring materials for inks. Since the polyhydric alcohol and formamide have high water solubility, however, the hydrolysis of the reactive dyes occurs more easily than the reaction with these polymers. Therefore, the synthesis itself is difficult, and moreover purification after synthesis is also difficult. Besides, since the reactive dyes undergo a reaction under alkaline conditions, the reactants must be kept at pH 11 to 12 with sodium hydroxide or the like. However, the use of such high-alkaline inks markedly limits materials for parts, with which the inks come into contact, in all recording including ink-jet recording, and besides causes a problem of safety. Therefore, such an ink must be neutralized with an acid. Further, in systems such as ink-jet systems, in which ink are passed through fine nozzles or tubes, a salt may be deposited in such nozzles or tubes in some cases, resulting in clogging. Therefore, treatments such as desalting are also required.
In Japanese Patent Application Laid-Open No. 62-119279, a specific reactive dye is reacted with polyethyleneimine having a molecular weight of from 10,000 to 70,000 to obtain a coloring material having good water fastness. When polyethyleneimine having such a high molecular weight is used, however, the reaction product with the dye becomes a giant molecule. Therefore, the viscosity of the resulting ink becomes high, and so ink-jet suitability of the ink, such as followability, is deteriorated. In addition, a proportion of chromophore in the molecule becomes low, so that the composition of the ink is limited. Further, the pH of the synthesized product becomes strongly alkaline due to an unreacted imino group, since the imino group shows strong alkalinity, so that inks using such a synthesized product as a coloring material also shows strong alkalinity. Therefore, when such a synthesized product is used, materials for parts, with which the resulting ink comes into contact, are markedly limited, and moreover a problem of safety arises. Therefore, it is necessary to make the pH of the ink neutral by conducting neutralization with an acid or reacting an excess amount of a reactive dye to the imino group. However, when the imino group is neutralized, the resulting dye compound loses water solubility. Therefore, a problem that the dye compound aggregates and precipitates has arisen.